Thermochemical regeneration with oxidant preheating

ABSTRACT

Employing furnace combustion gases for both thermochemical regeneration and heating of regenerators to preheat oxidant for the furnace provides synergistic efficiencies and other advantages.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/211,510, filed on Aug. 28, 2015, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to combustion in furnaces such asglassmelting furnaces, furnaces for heating and/or melting metals andores; incinerators; cement kilns; and the like, wherein material is fedinto the furnace and is heated and/or melted by the heat of combustionthat occurs within the furnace.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 6,113,874 discloses heat recovery methods useful withfurnaces employing regenerators wherein a stream of combustion productsformed in the furnace is passed through a first regenerator to heat thefirst regenerator and cool the combustion products, and then a portionof the cooled combustion products is combined with fuel to form amixture which is passed through a second heated regenerator wherein themixture undergoes an endothermic reaction to form syngas that thenpasses into the furnace and is combusted.

This patent mentions that some of the combustion products (“flue gas”)can be passed from the furnace through a separate regenerator to heatthis separate regenerator, following which technically pure oxygen canbe passed through this heated separate regenerator to heat the oxygenwhich is then fed from the regenerator into the furnace for combustion.

However, what is said in this patent to be the “optimal” amount ofcombustion products from combustion of syngas made from a mixture ofpure CH₄ and recycled flue gas and pure O₂ as oxidant to be passed fromthe furnace into this separate regenerator, relative to the amount ofthe combustion products to be passed from the furnace into the first orsecond regenerators that are used to provide heat for the endothermicreaction to form syngas, has been discovered by the present inventor tobe not at all optimal in terms of improving the overall efficiency ofthe operation. Indeed, the present inventor has found that significantlyimproved efficiency and energy utilization are available by utilizingconditions that are not taught or suggested by what this patentdiscloses about apportioning the flows of combustion products to theseparate regenerator relative to the flows to the first and secondregenerators. Indeed, the present inventor has determined a superiorbasis for apportioning the flows of combustion products to the separateregenerator relative to the flows to the first and second regenerators,and has found what is the optimal apportionment of these flows ofcombustion products. Furthermore, the present inventor has found apreferred method to apportion the flows of combustion products to theregenerators relative to the flows to the first and second regeneratorsfor different amounts of recycled flue gas mixed with the reformingfuel.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is a method of carrying outcombustion in a furnace, comprising

(A) combusting fuel in a furnace to produce gaseous combustion products,and(B) alternately (1) (i) passing a first amount of gaseous combustionproducts from the furnace into and through a cooled first regenerator toheat the first regenerator and cool said first amount of gaseouscombustion products,(ii) passing a second amount of gaseous combustion products from thefurnace into and through a cooled second regenerator to heat the secondregenerator and cool said second amount of gaseous combustion products,(iii) passing reforming fuel and (that is, with one or more of) at leasta portion of the cooled gaseous combustion products from said firstregenerator, at least a portion of the cooled gaseous combustionproducts from said second regenerator, or at least a portion of thecooled gaseous combustion products from both of said first and secondregenerators, into a heated third regenerator,(iv) reacting the gaseous combustion products and the reforming fuel inthe third regenerator in an endothermic reaction under conditionseffective to form syngas comprising hydrogen and carbon monoxide, andthereby cooling the third regenerator,(v) passing gaseous oxidant into and through a heated fourth regeneratorto heat the gaseous oxidant and cool the fourth regenerator, and(vi) passing said syngas from said third regenerator into said furnace,passing said heated gaseous oxidant from the fourth regenerator into thefurnace, and combusting the syngas and said heated gaseous oxidant inthe furnace;while maintaining (C1), (C2), or both (C1) and (C2):

(C1) maintaining the ratio of the molar flow rate of said first amountof cooled gaseous combustion products which is passed from said firstregenerator to the molar flow rate of said cooled second amount ofgaseous combustion products which is passed from said second regeneratorat from 45:55 to 65:35;

(C2) maintaining the difference in temperatures of the combustionproducts passing out of said first and second regenerators at 300 F orless; and

(2) (i) passing a first amount of gaseous combustion products from thefurnace into and through a cooled third regenerator to heat the thirdregenerator and cool said first amount of gaseous combustion products,

(ii) passing a second amount of gaseous combustion products from thefurnace into and through a cooled fourth regenerator to heat the fourthregenerator and cool said second amount of gaseous combustion products,(iii) passing reforming fuel and (that is, with one or more of) at leasta portion of the cooled gaseous combustion products from said thirdregenerator, at least a portion of the cooled gaseous combustionproducts from said fourth regenerator, or at least a portion of thecooled gaseous combustion products from both of said third and fourthregenerators, into a heated first regenerator,(iv) reacting the gaseous combustion products and the reforming fuel inthe first regenerator in an endothermic reaction under conditionseffective to form syngas comprising hydrogen and carbon monoxide, andthereby cooling the first regenerator,(v) passing gaseous oxidant into and through a heated second regeneratorto heat the gaseous oxidant and cool the second regenerator, and(vi) passing said syngas from said first regenerator into said furnace,passing said heated gaseous oxidant from the second regenerator into thefurnace, and combusting the syngas and said heated gaseous oxidant inthe furnace;while maintaining (D1), (D2), or both (D1) and (D2):

(D1) maintaining the ratio of the molar flow rate of said first amountof cooled gaseous combustion products which is passed from said firstregenerator to the molar flow rate of said cooled second amount ofgaseous combustion products which is passed from said second regeneratorat from 45:55 to 65:35;

(D2) maintaining the difference in temperatures of the combustionproducts passing out of said first and second regenerators at 300 F orless.

In a preferred embodiment of this aspect of the invention, at the end ofsteps (B) (1)(iii) and (B)(1)(v) the flows of said reforming fuel tosaid third regenerator and of said oxidant to said fourth regeneratorare terminated and gaseous combustion products from the furnace areflowed through said third and fourth regenerators so that syngas in thethird regenerator and oxidant in the fourth regenerator are expelled tothe furnace and combusted to completion, and at the end of steps (B)(2)(iii) and (B)(2)(v) the flows of said reforming fuel to said firstregenerator and of said oxidant to said second regenerator areterminated and gaseous combustion products from the furnace are flowedthrough said first and second regenerators so that syngas in the firstregenerator and oxidant in the second regenerator are expelled to thefurnace and combusted to completion.

Another aspect of the present invention is a method of carrying outcombustion in a furnace, comprising

(A) combusting fuel in a furnace to produce gaseous combustion products,and(B) alternately (1) (i) passing a first amount of gaseous combustionproducts from the furnace into and through a cooled first regenerator toheat the first regenerator and cool said first amount of gaseouscombustion products,(ii) passing a second amount of gaseous combustion products from thefurnace into and through a cooled second regenerator to heat the secondregenerator and cool said second amount of gaseous combustion products,(iii) passing reforming fuel into and through a heated third regeneratorto heat the reforming fuel and cool the third regenerator,(iv) passing gaseous oxidant into and through a heated fourthregenerator to heat the gaseous oxidant and cool the fourth regenerator,and(v) passing said heated reforming fuel from said third regenerator intosaid furnace, passing said heated gaseous oxidant from the fourthregenerator into the furnace, and combusting said heated reforming fueland said heated gaseous oxidant in the furnace;

while maintaining (C1), (C2), or both (C1) and (C2):

(C1) maintaining the ratio of the molar flow rate of said first amountof cooled gaseous combustion products which is passed from said firstregenerator to the molar flow rate of said cooled second amount ofgaseous combustion products which is passed from said second regeneratorat less than 65:35 and at least 45:55;

(C2) maintaining the difference in temperatures of the combustionproducts passing out of said first and second regenerators at 300 F orless; and (2) (i) passing a first amount of gaseous combustion productsfrom the furnace into and through a cooled third regenerator to heat thethird regenerator and cool said first amount of gaseous combustionproducts,

(ii) passing a second amount of gaseous combustion products from thefurnace into and through a cooled fourth regenerator to heat the fourthregenerator and cool said second amount of gaseous combustion products,(iii) passing reforming fuel into a heated first regenerator to heat thereforming fuel and cool the first regenerator,(iv) passing gaseous oxidant into and through a heated secondregenerator to heat the gaseous oxidant and cool the second regenerator,and(v) passing said heated reforming fuel from said first regenerator intosaid furnace, passing said heated gaseous oxidant from the secondregenerator into the furnace, and combusting said heated reforming fueland said heated gaseous oxidant in the furnace;

while maintaining (D1), (D2), or both (D1) and (D2):

(D1) maintaining the ratio of the molar flow rate of said first amountof cooled gaseous combustion products which is passed from said firstregenerator to the molar flow rate of said cooled second amount ofgaseous combustion products which is passed from said second regeneratorat less than 65:35 and at least 45:55;

(D2) maintaining the difference in temperatures of the combustionproducts passing out of said first and second regenerators at 300 F orless. In a preferred embodiment of this aspect of the invention, at theend of step (B) (1)(iii) the flow of said reforming fuel to said thirdregenerator is terminated and gaseous combustion products from saidfurnace are flowed or continue to flow through said third regeneratorinto the furnace to reduce the amount of soot present in the thirdregenerator, and wherein at the end of step (B) (2)(iii) the flow ofsaid reforming fuel to said first regenerator is terminated and gaseouscombustion products from said furnace are flowed or continue to flowthrough said first regenerator into the furnace to reduce the amount ofsoot present in the first regenerator.

By “at least a portion” or “some” is meant, an amount greater than 0%,and less than or equal to 100%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are schematic representations of different aspects of thepresent invention.

FIGS. 4 and 5 are graphs of flue gas temperature against flue gas flowratios obtained in accordance with the Example provided below.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is useful in furnaces such as glassmeltingfurnaces, furnaces for heating and/or melting metals and ores;incinerators; cement kilns; and the like, wherein material is fed intothe furnace and is heated and/or melted by the heat of combustion thatoccurs within the furnace. The combustion occurs between fuel, which canbe any combustible gaseous hydrocarbon or atomized liquid hydrocarbon(preferably comprising C1-C4 compounds such as methane) as well as thesyngas that is produced as described herein, and gaseous oxidant whichincludes air and any gaseous mixture containing more oxygen than air. Inthe accompanying FIG. 1, the additions of fuel and oxidant that mayoccur are represented as 11A and 11B respectively.

The present invention is described herein in particular detail withrespect to a preferred type of furnace, namely one that employs a heatrecovery process which recaptures usable heat from high temperature fluegas exhaust streams. This heat recovery process proceeds in two cycles,which are referred to herein as the flue cycle and the reforming cycle.These two cycles are performed alternatingly in two or morechecker-filled regenerators. The heat recovery process is preferablycarried out in association with furnaces and other combustion deviceswhich employ “oxy-fuel” combustion processes, by which is meantcombustion of fuel with gaseous oxidant comprising an oxygen content ofat least 50 vol. % oxygen, and preferably at least 80 vol. % oxygen,more preferably at least 90 vol. % oxygen, and even at least 99 vol. %oxygen, because the flue gases produced by oxy-fuel combustion havehigher H2O and CO2 concentrations, both of which promote the endothermicreforming reactions that are utilized in the method of this invention.During the flue cycle, the checkers in a first regenerator extract andstore heat from a high temperature flue gas which is fed from thefurnace into and through this regenerator. Then, in the reforming cycle,from the cooled flue gas that exits the first regenerator, a portion(which is referred to herein as Recycled Flue Gas or RFG) is fed intoanother regenerator and mixed with a stream of fuel (referred to hereinas Reforming Fuel or RF). In the following description, pure methane(CH4) is described as reforming fuel for purposes of illustration. Othersatisfactory reforming fuels include any combustible gas containingsignificant concentration of hydrocarbons, gas mixture, or vaporizedliquid fuels including, but not limited to, natural gas, propane, andLPG (liquefied petroleum gas). Fuels that predominantly comprise H2 andCO such as producer gas generated by gasifying coal are not suitable asReforming Fuel. Thus, the reforming fuel should comprise at least 25vol. % of one or more gaseous hydrocarbons of the formula CH₄ and/orC_(X)H_(Y) wherein X is 2-4 and Y is X to (4X−2). In the reformingcycle, the RFG/Reforming Fuel mixture enters the second regenerator inwhich the checker has already been heated, as described herein, andflows through it towards the furnace. The temperature of the RFG/RFmixture passing through the second regenerator continues to increase byextracting heat from the already pre-heated checker. As the RGF/RFmixture passes through the second regenerator, it reaches a temperatureat which thermal dissociation reactions and reforming reactions begin tooccur and continue to occur, producing products including H2 and CO.These reactions are endothermic and the heat needed to promote thesereactions is absorbed from the heated checker. Thermal dissociationreactions of fuel are known as cracking reactions and produce many fuelspecies such as H2, C2H2, C2H4, and soot. The reforming reactionsproduce a gaseous composition which typically comprises one or morecomponents such as such as H2, CO, and unreacted gases comprising H2O,CO2 and CH4. The gaseous composition thus produced may also be called“syngas” herein. The mixture of gaseous products emerges from the secondregenerator into the furnace wherein the combustible gaseous componentsare combusted with oxidant to provide thermal energy for heating and/ormelting material in the furnace. This combustion may combust a portionof any soot present with the gaseous products as well.

As described more fully below, gaseous oxidant for combustion in thefurnace is heated before it is fed into the furnace. It is heated bypassing it into and through a regenerator that has previously beenheated. At the same time, a portion of the gaseous combustion productsformed in the furnace are passed out of the furnace through anotherregenerator, to heat that regenerator.

After a length of time, the operation of the two regenerators isreversed, i.e., the regenerator that was used in the flue cycle isswitched to the reforming cycle, and the regenerator that was used inthe reforming cycle is switched to the flue cycle. Prior to the reversalthe flow of reforming fuel is stopped and the flow of RFG (recycled fluegas, that is, recycled gaseous combustion products) is continued untilsome or all of the residual reforming fuel and syngas in the regeneratorare purged out of the regenerator and combusted in the furnace. Asdescribed further below, this purging step also acts to remove sootdeposited on checker surfaces in the regenerator as soot reacts with RFGand is gasified. Upon this reversal, the regenerator that was heated byoutgoing flue gas is switched to start heating incoming oxidant, and theregenerator that was used to heat incoming oxidant is switched so thatflue gas exiting the furnace passes through it in order to reheat it foruse in heating oxidant. After a further period of time, the operation ofthe two pairs of regenerators is reversed again. The timing of thereversals can be determined by elapsed time, or by other criteria suchas the temperature of the flue gas exiting from the first regeneratorthat is in flue cycle. The reversal process is carried out according toa predetermined mechanism and plan, wherein valves are sequenced to openand close based on specific timings.

The operation and control of the present invention is described below inconjunction with FIGS. 1 to 3. An end-port fired glass furnace (10)fitted with two regenerators in end wall (3) is used as an example.

As shown in FIG. 1, end-port glass furnace (10) has a feed station (20)where feed material (30) comprising solid glassmaking materials (knownas batch and/or cullet) are charged into the furnace to be heated andmelted. The flow of molten glass out of furnace (10) is represented as(90). The furnace (10) is equipped with first regenerator (100) on thefurnace left side and second regenerator (200) on the furnace rightside. Vertical cross-sectional views of the two regenerators aredisplayed in more detail in FIGS. 2 and 3.

As seen in FIG. 2, regenerator (200) is in the flue cycle wherein fluegas stream (50) from the interior of furnace (10) enters port neck (240)and then flows to the top space (530) of regenerator (200) past anoxygen analyzer (250). The flue gas stream heats checkers (representedas (520)) as it flows through passages between the checkers withinregenerator (200), and enters chamber bottom space (500) through gaspassages (515) supported on arch (510) which also supports the weight ofthe whole bed of checkers. As seen in FIG. 1, a portion (52) of the fluegases produced in furnace (10) may be by-passed to conduit (70) througha partially opened valve (350) then enters stack (340) to exhaust, bywhich is meant that it does not re-enter the furnace but instead isdischarged to the atmosphere and/or conveyed to one or more otherstations for storage and/or further treatment or any combination of suchdestinations. For maximum heat recovery, it is preferred that valve(350) is closed so that essentially all the furnace flue gas goes toregenerator (200) as flue gas stream (50).

As seen in FIGS. 1 and 2, the cooled flue gas stream (201) exits theregenerator (200) in conduit (260), passes through an open valve (210)and oxygen sensor (310), and then enters the suction-side of blower(300). The majority of the flue gas (301) leaving the pressure-side ofthe blower passes through a damper (330) then a flow meter (332), andfinally is directed into stack (340) through which this flue gas leavesthe system to exhaust as defined herein. A portion (303) of the flue gasis recycled to the bottom of regenerator (100) by passing throughconduit (320) and valve (360). This is Recycled Flue Gas (RFG). Its flowis metered by a flow meter (322). Reforming fuel which is to be fed tothe second regenerator (100) is supplied by a conduit (130) throughvalve (120).

Suitable reforming fuels include methane (which is preferred) as well asany other combustible gas, gas mixture, or vaporized liquid fuelsincluding, but not limited to, natural gas, propane, and LPG (liquefiedpetroleum gas).

As seen in FIG. 3, the reforming fuel (RF) from conduit (130) intersectsand mixes with the RFG (303) at location (127) in conduit (128) whichalso communicates with the bottom space (400) of regenerator (100). ThisRFG/RF mixture enters the already pre-heated checker pack (420) ofregenerator (100) through gas passages (415) on arch (410). Regenerator(100) has already been heated in a previous cycle by passage of flue gasfrom the furnace into and through the regenerator (100). The temperatureof the RFG/RF mixture increases as it flows through the checker pack ofregenerator (100). When the temperature of the RFG/RF becomessufficiently high, thermal dissociation reactions and endothermicreforming reactions occur in which the reforming fuel (e.g. CH4) reactswith CO2 and H2O in the RFG and forms CO, H2, and possibly some soot.The required heat for the endothermic dissociation and reformingreactions is taken from the heated checkers. The reforming reactioncontinues as the RFG/RF mixture continues to travel toward the top space(430). The gaseous stream (425) (referred to herein as a “reformed” or“syngas” gas stream) exits from the top of checker pack (420). Stream(425) has high temperature and includes species such as CO, H2,unreacted CH4, and unreacted CO2 and H2O. The stream (425) passesthrough port neck (140) and oxygen sensor (150), and enters furnace(10). This stream exits checker pack (420) at temperatures for exampleranging from 1800 F to 2500 F.

In this cycle of operation, referring to FIGS. 1 and 3, heated oxidantfor combustion of the syngas is supplied to furnace (10) through conduit(135). The oxidant can be air, or it can have an oxygen content higherthan that of air, i.e. at least 21 vol. %, and preferably equal to orhigher than 80 vol. %, more preferably equal to or higher than 90 vol.%, or even at least 99 vol. %. The oxidant is provided from a suitablesource such as a storage tank or an air separation unit (examples ofwhich are known and commercially available) through conduit (605) andinto and through heated regenerator (600). Regenerator (600) can havethe customary structure and mode of operation in which checker pack(691) is supported on arch (692) through which gas passages (693) arepresent that permit gas to flow between the checker pack (691) andbottom space (694). In this cycle of operation, gaseous oxidant flowsfrom line (606) into bottom space (694), into and through checker pack(691), to top space (695) and into line (135). The oxidant is heated inregenerator (600) and passes from regenerator (600) into conduit (135)and into the furnace. Valve (115) is open to permit flow of oxidant intoline (606) through which oxidant passes into regenerator (600). Valve(620), which controls flow of flue gas through and out of regenerator(600) into conduit (610) which is connected to the inlet (suction-side)of blower (300), is closed in this cycle. In the other cycle, describedherein, the valve positions are reversed, and flue gas flows from line(135) into and through regenerator (600) in the opposite path to line(606).

In this cycle of operation, referring to FIGS. 1 and 2, some of thegaseous combustion products (flue gas) passes out of the furnace (10)into conduit (235) and thence into and through regenerator (700).Regenerator (700) can have the customary structure and mode of operationin which checker pack (791) is supported on arch (792) through which gaspassages (793) are present that permit gas to flow between the checkerpack (791) and bottom space (794). This flow of combustion products fromline (235) heats regenerator (700). The combustion products are cooledand exit regenerator (700) via conduit (710) and then enter the inlet(suction-side) of blower (300). Valve (720), which controls flow of fluegas through and out of regenerator (700) into conduits (710) and (721),is open in this cycle, and valve (225) which controls flow of oxidantfrom a suitable source such as a storage tank or an air separation unitfrom conduit (705) into and through heated regenerator (700) in the nextcycle, is closed. In the other cycle, described herein, the valvepositions are reversed, and flue gas flows from line (237) into andthrough regenerator (700) in the opposite path to line (235) and intofurnace (10).

Typically, the heat recovery process proceeds with one of theregenerators (100) and (200) in the flue cycle and one of theseregenerators in the reforming cycle, as seen in FIG. 1, and with one ofthe oxidant regenerators (600) and (700) in oxidant-heating mode and onebeing reheated by flue gas passing through it, for about 20 to 40minutes or until the checkers in the reforming regenerator are too coldto provide sufficient heat to promote the desired endothermic chemicalreactions. At that point, and now continuing with the description hereinwhere regenerator (200) was in the flue cycle and regenerator (100) wasin the reforming cycle, and oxidant was heated in regenerator (600) andfed into the furnace while gaseous combustion products were leavingfurnace (10) and heating regenerator (700), the operation of furnace(10) undergoes reversal in which regenerator (200) is transitioned tothe reforming cycle for heat recovery, regenerator (100) is transitionedinto the flue cycle for heat accumulation, regenerator (600) istransitioned to receive flue gas in order to reheat regenerator (600),and regenerator (700) is transitioned to receive and heat oxidantpassing through it into the furnace.

Before the reversal, remaining syngas in regenerator (100) and remainingoxidant in regenerator (600) are to be purged to furnace (10). In thisinstance, reforming fuel supplied to the regenerator (100) and oxidantsupplied to regenerator (600) are terminated at first by closing valve(120) and valve (115) respectively and opening oxidant purge line valve(365) to let RFG from blower (300) flow through lines (320) and (305)through valve (365) to line (606). Remaining syngas in regenerator (100)and remaining oxidant in regenerator (600) are purged by the RFG for aspecified amount of time so that all or nearly all the syngas in theregenerator (100) and all or nearly all of the oxidant in regenerator(600) are expelled to the furnace and combusted to completion. Flowing,or continuing the flow, of gaseous combustion products throughregenerators (100) and (600), also aids in removing soot that may haveaccumulated within the regenerators as a byproduct of reformingreactions and/or thermal cracking of the substances fed into theregenerators. Soot removal occurs by gasification reactions withreactants that may be present in the gaseous combustion products (RFG)such as O2, dissociated oxygen species, carbon dioxide, and/or watervapor.

Upon reversal, the flue gas from the furnace passes through regenerator(100), and a portion thereof passes to exhaust (as defined herein) whilea portion or the balance is mixed with fuel and the mixture is passedthrough regenerator (200) and into the furnace. Valve (110) which hadbeen closed is opened, valve (210) is closed, and valve (360) is closedand valve (380) which had been closed is opened, to permit heated fluegas to pass from regenerator (100) toward and through blower (300), andto permit a portion (303) of this flue gas to pass into regenerator(200) after it is mixed with reforming fuel (230) which enters throughvalve (220) which had been closed but now is opened. Valve (115) whichhad been open is closed, as no combustion aided by oxidant through valve(115) occurs in this phase, and valve (225) is opened. The resultingmixture of reforming fuel and recycled flue gas undergoes in regenerator(200) the endothermic reforming reactions which had occurred inregenerator (100) in the previous cycle as described herein, to producesyngas which passes into and through port neck (240) and then intofurnace (10) where it is combusted with oxidant from conduit (237) thathas been heated after being fed through valve (225). In addition, uponreversal, flue gas passes through regenerator (600) and the flow ofoxidant through regenerator (600) is shut off, whereas flow of flue gasfrom the furnace through regenerator (700) is shut off and flow ofoxidant through regenerator (700) into the furnace commences. Valves(115) and (720) are closed, and valves (620) and (225) are opened.

Before the reversal, remaining syngas in regenerator (200) and remainingoxidant in regenerator (700) are to be purged to furnace (10). In thisinstance, reforming fuel supplied to the regenerator (200) and oxidantsupplied to regenerator (700) are terminated at first by closing valve(220) and valve (225) respectively and opening oxidant purge line valve(385) to let RFG flow from blower (300) from line (301) through line(307) to lines (710) and (701). Remaining syngas in regenerator (200)and remaining oxidant in regenerator (700) are purged by the RFG for aspecified amount of time so that nearly all the syngas in theregenerator (200) and all of the oxidant in regenerator (700) areexpelled to the furnace and combusted to completion.

Thus it can be seen that in one cycle, recycled flue gas (721) that isfed with reforming fuel (130) to regenerator (100) can comprise recycledflue gas from regenerator (200), recycled flue gas from regenerator(700), or recycled flue gas from both regenerators (200) and (700). Inthe other cycle, recycled flue gas (610) that is fed with reforming fuel(230) to regenerator (200) can comprise recycled flue gas fromregenerator (100), recycled flue gas from regenerator (600), or recycledflue gas from both regenerators (100) and (600).

During the heat recovery process, furnace (10) may be co-fired withother burners such as (60) and (65) such that both syngas flame (40) andburner flames (62) and (64) co-exist. In addition, burners (60) and (65)may or may not be firing during the reversal process when the reformingregenerator (100) or (200) as the case may be is undergoing the purgingsequence described above. For maximum heat recovery, it is preferredthat burners (60) and (65) are not co-firing with the syngas flame (40).It is also preferred that during the purging sequence, burners (60) and(65) are not firing.

The present invention utilizes the above-described apparatus to attainunexpected objectives, by operating in accordance with guidelines thathave not previously been recognized.

As indicated, in each cycle gaseous combustion products are beingwithdrawn from the furnace and passed in parallel through each of a pairof regenerators, with one portion of the gaseous combustion productsbeing passed through a regenerator to provide heat to the regeneratorthat will in the next cycle heat the mixture of combustion products andfuel to be reformed in the endothermic reforming reaction, and withanother portion of the gaseous combustion products being passed througha regenerator to provide heat to the regenerator that will in the nextcycle heat gaseous oxidant that is passed through the regenerator intothe furnace.

It has been unexpectedly discovered that in each such cycle, the pair ofregenerators through which gaseous combustion products are passed shouldbe operated so as to maintain either or both of two sets of conditions.One set of conditions is that the ratio between the molar flow rate ofthe gaseous combustion products flowing from the regenerator that willbe used to provide heat to the endothermic reaction in the next cycle,and the molar flow rate of the gaseous combustion products flowing fromthe regenerator that will be used to preheat oxidant that will be heatedand passed into the furnace in the next cycle, should be maintained sothat this ratio is less than 70:30 when the RFG/RF molar ratio is 1:1and the ratio of the molar flue gas flow rate to the molar RFG/RFmixture flow rate is 2:1. Preferably this ratio is less than 65:45, andat least 55:45. A more preferred range for this ratio is (57 to 65):(43to 35).

Contrary to the prior teaching of U.S. Pat. No. 6,113,874 the presentinventor has also discovered that it is advantageous to operate thereforming regenerator at RFG/RF molar ratio below 0.5, or even withoutRFG flow, i.e., at RFG/RF molar ratio of 0, when oxidant to be fed intothe furnace is heated in a separate regenerator that has been heated byflowing flue gas through it from the furnace. When no RFG is mixed withRF, no reforming reactions can take place; however, some of the fuelcomponents will crack to form hydrogen, C₂H₄, C₂H₂, soot, and many otherspecies. These cracking reactions are also endothermic and contribute tothe recovery of heat into the gaseous species from the regenerator. Whenno recycled flue gas is mixed with “reforming fuel”, the ratio betweenthe molar flow rate of the gaseous combustion products flowing from theregenerator that was used to heat the regenerator and thus provide heatto the endothermic reaction in the next cycle, and the molar flow rateof the gaseous combustion products flowing from the regenerator that wasused to preheat oxidant that will be heated and passed into the furnacein the next cycle, should be maintained so that this ratio is less than65:35. Preferably this ratio is less than 60:40, and more preferably atleast 50:50. A more preferred range for this ratio is (55 to 60):(45 to40).

It is particularly advantageous that the total amount of combustionproducts exiting the furnace are those in the two ducts feedingcombustion products into the regenerators. The desired relationshipbetween the respective molar flow rates can be monitored and implementedby appropriate metering devices in the conduit placed downstream of eachregenerator, and by appropriate setting of the valves that regulate therate of flow of gases in each conduit. For instance, in one cycle thesemolar flow rates are those in conduit (201) and (710), so (as willalready have been recognized from the description herein and the FIGS.1-3) the desired adjustments in the flow rates would be established bysetting the valves (210) and (720) to positions between full-flow andshut-off that permit the desired rates of flow that would achieve thedesired molar flow ratios or the desired relatively close temperaturesof the respective streams, as described herein. Similarly, in the othercycle these molar flow rates are those in conduits (128) and (621), sothe control would be effected by settings of valves (110) and (620).

Another set of conditions to maintain in accordance with the presentinvention is to provide that the temperatures of the flows of gaseouscombustion products exiting each pair of regenerators through whichcombustion products flow in each alternating cycle (that is, referringto FIG. 1, regenerators (200) and (700) in one cycle, and regenerators(100) and (600) in the other cycle, should be within 300 F or less ofeach other, preferably within 200 F, and more preferably within 100 F orless of each other. Stated another way, the temperature differencebetween these two flows of gaseous combustion products should be 300 For less, preferably 200 F or less, more preferably 100 F or less.Referring to FIG. 1, this refers to the difference between thetemperatures of streams (201) and (710) in one cycle, and the differencebetween the temperatures of streams (128) and (621) in the other cycle.These temperatures can readily be measured and compared using equipmentthat is conventional and commercially available. One advantageous mannerfor maintaining the respective temperature differences within theindicated proximity to each other is by adjusting the molar flow ratesof each of the streams of combustion products from the furnace into andthrough each regenerator that is heated by the combustion products in agiven cycle.

Typical temperatures are provided here for operation of the inventionwith a glassmaking furnace. The temperatures may be somewhat lower whenthe invention is operated with other types of furnaces such as steelreheating furnaces.

Referring to the cycle described with respect to FIGS. 1-3, flue gasstream (240) entering regenerator (200) is typically at 2500 F to 3000F, and stream (201) exiting regenerator (200) is typically at 500 F to1000 F. Stream (235) entering regenerator (700) is also typically at2500 F to 3000 F, and stream (701) exiting regenerator (700) istypically at 500 F to 1000 F. Stream (128) of mixed recycled flue gasand reforming fuel entering regenerator (100) is typically at 300 F to1000 F, and stream (140) of reformed product is typically at 1800 F to2400 F. Stream (606) of oxidant entering regenerator (600) is typicallyat zero degrees F. or ambient temperature, up to 100 F. Stream (135) ofheated oxidant exiting regenerator (600) is typically at 1800 F to 2400F.

The temperatures within each regenerator will be expected to rise andfall through each cycle, and the temperatures will be different atdifferent locations within the regenerators. In the typical operation ofthe invention with a glassmelting furnace, in the cycle depicted inFIGS. 1-3, the temperatures within regenerator (200) at the start of thecycle may be on the order of 500 F to 900 F at the bottom of theregenerator and 1800 F to 2300 F at the top, and may be expected to riseby the end of this cycle to temperatures on the order of 600 F to 1000 Fat the bottom and 1900 F to 2400 F at the top. In the same cycle, thetemperatures within regenerator (700) at the start of the cycle may beon the order of 500 F to 900 F at the bottom of the regenerator and 1800F to 2300 F at the top, and may be expected to rise by the end of thiscycle to temperatures on the order of 600 F to 1000 F at the bottom and1900 F to 2300 F at the top. In the same cycle, the temperatures withinregenerator (100) at the start of the cycle may be on the order of 600 Fto 1000 F at the bottom of the regenerator and 1900 F to 2400 F at thetop, and may be expected to be cooled by the end of this cycle totemperatures on the order of 500 F to 900 F at the bottom and 1800 F to2300 F at the top. In the same cycle, the temperatures withinregenerator (600) at the start of the cycle may be on the order of 600 Fto 1000 F at the bottom of the regenerator and 1900 F to 2400 F at thetop, and may be expected to be cooled by the end of this cycle totemperatures on the order of 500 F to 900 F at the bottom and 1800 F to2300 F at the top.

These figures would be expected if the cycle is reversed approximatelyevery 20 minutes. When the cycle is reversed less often, the differencebetween the temperatures at the beginning and end of each cycle (100 Fin this example) would be expected to be larger, and even twice, i.e.,about 200 F, as large as these figures if the cycles are reversed halfas often, that is, every 40 minutes.

Example

The following table shows approximate gas flow rates per one molar flowof fuel (CH₄ or natural gas [NG]) for a container glass furnace using asfeed material 30% cullet and 70% batch. Heating and melting the feedmaterials generates about one mole of batch gases in the furnace permole of fuel fed to the furnace. Batch gases are predominantly CO₂decomposed from carbonate materials in the batch and H₂O evaporated fromthe moisture in the batch and cullet fed to the furnace. The flue gasflow rate (5 moles) from a glass furnace equipped with thethermochemical regenerator system described herein includingregenerators (100) and (200) (referred to in this Example as “TCR”)which uses recycled flue gas (RFG) is much greater than the flue gasflow rate (3 moles) generated from combustion of fuel (CH₄) and pure O₂alone.

Approximate Gas Flow ratios (molar) Fuel (CH4) 1 Oxidant (100% O2) 2Combustion Flue gas 3 (CO2 + 2H2O) Batch gases (CO2, H2O) 1 Flue gaswith no RFG 4 Recycled flue gas 1 (RFG) Flue gas with RFG 5

In order to find the optimum flow ratio of flue gas from the furnaceinto the TCR and into the 02 regenerators (600) and (700), two separateheat exchanger models were set up, one for the TCR and the other for the02 regenerator. The maximum heat recovery from the flue gas, i.e., themost efficient operation, is achieved when the total sensible heatcontained in the two flue gas streams exiting the two regenerators isminimized. In FIGS. 4 and 5 the flue gas exit temperatures from the TCRregenerators and from the 02 regenerators and the average temperature ofthe combined stream when the two streams are mixed after the exiting theregenerators (i.e., molar flow weighted average flue gas temperature)are plotted against the portion (in molar percent) of the total flue gasflow directed to the TCR regenerators. The flue gas exit temperaturefrom the TCR regenerators increases as more flue gas is directed to theTCR. The flue gas exit temperature from the O₂ regenerators, on theother hand, decreases with increasing flue gas flow to the TCR. Sincethe total sensible heat in the combined stream is approximatelyproportional to the average temperature of the combined stream, theoptimum ratio of the flue gas flow to the TCR regenerators is located atthe point where the average flue gas temperature becomes the minimumvalue.

FIG. 4 represents a case at RFG/NG=1 (molar). The optimum flow ratio(that is, the molar percentage) of the flue gas that is fed to the TCRwith the balance being fed to the O₂ regenerator) which gives the lowestaverage flue gas exit temperature of the combined streams is about 62%in this case. It does not change much when the flue gas flow ratio tothe TCR is between 55 to 70% and below about 800 F in this example. Atthe flue gas flow ratio to the TCR of 55% the flue gas exit temperaturefrom the O₂ regenerator is about 300 F hotter than the flue gastemperature from the TCR. At the flue gas flow ratio to the TCR of 70%the flue gas exit temperature from the O₂ regenerator is about 300 Fcolder than the flue gas temperature from the TCR. At the flue gas flowratio to the TCR of about 61% the flue gas exit temperatures from thetwo regenerators are equal. This point is very close to the optimum flowrate. Since it is easier and more reliable to measure temperature by athermocouple than to measure the flow rate of flue gas containing stickyparticulates, the preferred method in this invention is to find a nearoptimum flow gas flow ratio by measuring the flue gas exit temperatureor the regenerator bottom temperature of each regenerator and adjustingthe flow rates to the TCR and to the O₂ regenerator until the twotemperatures are within about 300 F, preferably within 200 F, and morepreferably within 100 F. Alternatively a single thermocouple located inthe downstream conduit, after the two flue gas streams have been fullymixed, can be used to find the minimum flue gas temperature. Thismethod, however, is not sensitive to the change in the flow rates to theTCR and to the O₂ regenerator.

FIG. 5 represents the case with no recycled flue gas used for reformingreactions (i.e, RFG/RF=0). The optimum flow ratio to the TCR that givesthe lowest average flue gas exit temperature of the combined streams isabout 58% in this example. The average flue gas exit temperature of thecombined streams does not change much when the flue gas flow ratio tothe TCR is between 50 to 65% and below about 800 F in this case. At theflue gas flow ratio to the TCR of 50% the flue gas exit temperature fromthe O₂ regenerator is about 100 F hotter than the flue gas temperaturefrom the TCR. At the flue gas flow ratio to the TCR of 65% the flue gasexit temperature from the O₂ regenerator is about 500 F colder than theflue gas temperature from the TCR. At the flue gas flow rate to the TCRof about 53% the flue gas exit temperatures from the two regeneratorsare equal. This point is 5% less than the optimum flow rate, but theheat recovery efficiency is very close to that of the optimum flow rate.

Thus the practical method to find a near optimum flue gas flow ratiofound for the previous case is also applicable in this case.

The above examples indicate that the optimum flow ratio depend on fuelcomposition, oxidant composition, RFG/NG ratio, and batch/cullet ratio.However for a large change of RFG/NG ratio of 0 to 1 the optimum flowratio was found to be similar.

It has been discovered that operating in a manner that maintains theratio of molar flow rates of combustion product streams entering therespective regenerators, or that maintains the indicated controlleddifference in the temperatures of the flows of combustion productsexiting the respective regenerators, or that maintains bothrelationships (i.e. the molar flow rate ratio, and the temperaturedifference of the streams as described), attains superior heat recoveryand efficiency of energy utilization (storage and reuse in eachregenerator) that is superior to what appears to be suggested oravailable in the prior art such as the aforementioned U.S. Pat. No.6,113,874 wherein optimal heat efficiency was taught as requiringoperation under conditions which when analyzed correspond to theaforementioned ratio of molar flow rates being not less than 70:30.However, the present invention is all the more unexpected in that theaforementioned patent did not ascribe any particular recognition to thisratio of molar flow rates nor to the significance of the relationshipbetween the temperatures of the respective flows of combustion products.

In the preceding sections the present invention is described under thepreferred conditions that all of the fuel, as methane (CH4), and all ofthe oxidant, as industrially pure (at least 99.9 vol. % pure) oxygen,that are introduced into the furnace are heated or reformed in theregenerators. For cases in which some of the fuel and/or some of theoxidant are introduced into the furnace without having been heated orreformed in regenerators, and for cases in which the oxygenconcentration of the oxidant is less than 99.9%, the optimum ratio ofthe molar flow rates of the gaseous combustion products (flue gas) fromthe furnace through the first and second regenerators, and the optimumratio of the molar flow rates of the gaseous combustion products fromthe third and fourth regenerators (for passage into the reforming andoxidant-heating regenerators) changes from the optimum ratios for thepreferred conditions mentioned above. For example if 30% of thecombustion oxidant is injected into the furnace directly withoutpreheating (for instance, for a staged combustion to reduce NOxemission), the flow rate of oxidant into the oxidant-preheatingregenerators is reduced by that 30%. In this case the flow rate of fluegas into the oxidant-preheating regenerators should be reduced by about20 to 25% and the flow rate of flue gas into the reforming regeneratorshould be increased by that amount. Thus, the optimum ratio of the molarflow rates of the flue gas from the furnace through the firstregenerator relative to the molar flow rate through the secondregenerator, and through the third regenerator relative to the fourthregenerator, to be passed into the reforming and oxidant-heatingregenerators, is increased. An opposite example is found in the use oflow purity oxidant. If the oxygen purity of the oxidant used in themethod of the invention is for example 80 vol. % and all of this oxidantis preheated in the regenerators, then the flow rate of the oxidant is25% more than the case with pure oxygen as oxidant. In this case theflow rate of flue gas into the oxidant-preheating regenerators should beincreased by about 30 to 35% and the flow rate of flue gas into thereforming regenerator should be decreased by that amount. Thus, theoptimum ratio of the molar flow rates of flue gas from the furnacethrough the first regenerator relative to that of the secondregenerator, and the optimum ratio of the molar flow rates through thethird regenerator relative to that of the fourth regenerator, forpassing into the reforming regenerator and into the oxidant-heatingregenerators, is reduced.

These examples show that the optimum flow ratio of flue gas molar flowrates from the furnace into the reforming regenerator and into theoxidant-heating regenerators may vary considerably depending on theamount and compositions of the fuel, of the recycled gaseous combustionproducts (RFG), and of the oxidant available for preheating/reforming inthe regenerators. Thus the practical and preferred method in thisinvention is to establish the desired ratio of the flow rates bymeasuring the temperatures of the flue gas exiting the respectiveregenerators (or measuring the temperatures at the exit of theregenerators, which corresponds to the temperatures of the gas streamsthemselves), and adjusting the flow rates of the streams entering thefirst and second regenerators (in one cycle) and of the streams enteringthe third and fourth regenerators (in the other cycle) until the twotemperatures are within about 300 F, preferably within 200 F, and morepreferably within 100 F.

What is claimed is:
 1. A method of carrying out combustion in a furnace,comprising (A) combusting fuel in a furnace to produce gaseouscombustion products, and (B) alternately (1) (i) passing a first amountof gaseous combustion products from the furnace into and through acooled first regenerator to heat the first regenerator and cool saidfirst amount of gaseous combustion products, (ii) passing a secondamount of gaseous combustion products from the furnace into and througha cooled second regenerator to heat the second regenerator and cool saidsecond amount of gaseous combustion products, (iii) passing reformingfuel with cooled gaseous combustion products from said firstregenerator, with cooled gaseous combustion products from said secondregenerator, or with cooled gaseous combustion products from both ofsaid first and second regenerators, into a heated third regenerator,(iv) reacting the gaseous combustion products and the reforming fuel inthe third regenerator in an endothermic reaction under conditionseffective to form syngas comprising hydrogen and carbon monoxide, andthereby cooling the third regenerator, (v) passing gaseous oxidant intoand through a heated fourth regenerator to heat the gaseous oxidant andcool the fourth regenerator, and (vi) passing said syngas from saidthird regenerator into said furnace, passing said heated gaseous oxidantfrom the fourth regenerator into the furnace, and combusting the syngasand said heated gaseous oxidant in the furnace; while maintaining thedifference in temperatures of the combustion products passing out ofsaid first and second regenerators at 300 F or less; and (2) (i) passinga first amount of gaseous combustion products from the furnace into andthrough a cooled third regenerator to heat the third regenerator andcool said first amount of gaseous combustion products, (ii) passing asecond amount of gaseous combustion products from the furnace into andthrough a cooled fourth regenerator to heat the fourth regenerator andcool said second amount of gaseous combustion products, (iii) passingreforming fuel with cooled gaseous combustion products from said thirdregenerator, with cooled gaseous combustion products from said fourthregenerator, or with cooled gaseous combustion products from both ofsaid third and fourth regenerators, into a heated first regenerator,(iv) reacting the gaseous combustion products and the reforming fuel inthe first regenerator in an endothermic reaction under conditionseffective to form syngas comprising hydrogen and carbon monoxide, andthereby cooling the first regenerator, (v) passing gaseous oxidant intoand through a heated second regenerator to heat the gaseous oxidant andcool the second regenerator, and (vi) passing said syngas from saidfirst regenerator into said furnace, passing said heated gaseous oxidantfrom the second regenerator into the furnace, and combusting the syngasand said heated gaseous oxidant in the furnace; while maintaining thedifference in temperatures of the combustion products passing out ofsaid third and fourth regenerators at 300 F or less.
 2. A method ofcarrying out combustion in a furnace, comprising (A) combusting fuel ina furnace to produce gaseous combustion products, and (B) alternately(1) (i) passing a first amount of gaseous combustion products from thefurnace into and through a cooled first regenerator to heat the firstregenerator and cool said first amount of gaseous combustion products,(ii) passing a second amount of gaseous combustion products from thefurnace into and through a cooled second regenerator to heat the secondregenerator and cool said second amount of gaseous combustion products,(iii) passing reforming fuel with cooled gaseous combustion productsfrom said first regenerator, with cooled gaseous combustion productsfrom said second regenerator, or with cooled gaseous combustion productsfrom both of said first and second regenerators, into a heated thirdregenerator, (iv) reacting the gaseous combustion products and thereforming fuel in the third regenerator in an endothermic reaction underconditions effective to form syngas comprising hydrogen and carbonmonoxide, and thereby cooling the third regenerator, (v) passing gaseousoxidant into and through a heated fourth regenerator to heat the gaseousoxidant and cool the fourth regenerator, and (vi) passing said syngasfrom said third regenerator into said furnace, passing said heatedgaseous oxidant from the fourth regenerator into the furnace, andcombusting the syngas and said heated gaseous oxidant in the furnace;while maintaining the ratio of the molar flow rate of said cooled firstamount of gaseous combustion products which is passed from said firstregenerator to the molar flow rate of said cooled second amount ofgaseous combustion products which is passed from said second regeneratorat from 45:55 to 65:35; and (2) (i) passing a first amount of gaseouscombustion products from the furnace into and through a cooled thirdregenerator to heat the third regenerator and cool said first amount ofgaseous combustion products, (ii) passing a second amount of gaseouscombustion products from the furnace into and through a cooled fourthregenerator to heat the fourth regenerator and cool said second amountof gaseous combustion products, (iii) passing reforming fuel with cooledgaseous combustion products from said third regenerator, with cooledgaseous combustion products from said fourth regenerator, or with cooledgaseous combustion products from both of said third and fourthregenerators, into a heated first regenerator, (iv) reacting the gaseouscombustion products and the reforming fuel in the first regenerator inan endothermic reaction under conditions effective to form syngascomprising hydrogen and carbon monoxide, and thereby cooling the firstregenerator, (v) passing gaseous oxidant into and through a heatedsecond regenerator to heat the gaseous oxidant and cool the secondregenerator, and (vi) passing said syngas from said first regeneratorinto said furnace, passing said heated gaseous oxidant from the secondregenerator into the furnace, and combusting the syngas and said heatedgaseous oxidant in the furnace; while maintaining the ratio of the molarflow rate of said cooled first amount of gaseous combustion productswhich is passed from said third regenerator to the molar flow rate ofsaid cooled second amount of gaseous combustion products which is passedfrom said fourth regenerator at from 45:55 to 65:35.
 3. A method ofcarrying out combustion in a furnace, comprising (A) combusting fuel ina furnace to produce gaseous combustion products, and (B) alternately(1) (i) passing a first amount of gaseous combustion products from thefurnace into and through a cooled first regenerator to heat the firstregenerator and cool said first amount of gaseous combustion products,(ii) passing a second amount of gaseous combustion products from thefurnace into and through a cooled second regenerator to heat the secondregenerator and cool said second amount of gaseous combustion products,(iii) passing reforming fuel into and through a heated third regeneratorto heat the reforming fuel and cool the third regenerator, (iv) passinggaseous oxidant into and through a heated fourth regenerator to heat thegaseous oxidant and cool the fourth regenerator, and (v) passing saidheated reforming fuel from said third regenerator into said furnace,passing said heated gaseous oxidant from the fourth regenerator into thefurnace, and combusting said heated reforming fuel and said heatedgaseous oxidant in the furnace; while maintaining the difference intemperatures of the combustion products passing out of said first andsecond regenerators at 300 F or less; and (2) (i) passing a first amountof gaseous combustion products from the furnace into and through acooled third regenerator to heat the third regenerator and cool saidfirst amount of gaseous combustion products, (ii) passing a secondamount of gaseous combustion products from the furnace into and througha cooled fourth regenerator to heat the fourth regenerator and cool saidsecond amount of gaseous combustion products, (iii) passing reformingfuel into a heated first regenerator to heat the reforming fuel and coolthe first regenerator, (iv) passing gaseous oxidant into and through aheated second regenerator to heat the gaseous oxidant and cool thesecond regenerator, and (v) passing said heated reforming fuel from saidfirst regenerator into said furnace, passing said heated gaseous oxidantfrom the second regenerator into the furnace, and combusting said heatedreforming fuel and said heated gaseous oxidant in the furnace; whilemaintaining the difference in temperatures of the combustion productspassing out of said first and second regenerators at 300 F or less.
 4. Amethod of carrying out combustion in a furnace, comprising (A)combusting fuel in a furnace to produce gaseous combustion products, and(B) alternately (1) (i) passing a first amount of gaseous combustionproducts from the furnace into and through a cooled first regenerator toheat the first regenerator and cool said first amount of gaseouscombustion products, (ii) passing a second amount of gaseous combustionproducts from the furnace into and through a cooled second regeneratorto heat the second regenerator and cool said second amount of gaseouscombustion products, (iii) passing reforming fuel into and through aheated third regenerator to heat the reforming fuel and cool the thirdregenerator, (iv) passing gaseous oxidant into and through a heatedfourth regenerator to heat the gaseous oxidant and cool the fourthregenerator, and (v) passing said heated reforming fuel from said thirdregenerator into said furnace, passing said heated gaseous oxidant fromthe fourth regenerator into the furnace, and combusting said heatedreforming fuel and said heated gaseous oxidant in the furnace; whilemaintaining the ratio of the molar flow rate of said first amount ofcooled gaseous combustion products which is passed from said firstregenerator to the molar flow rate of said cooled second amount ofgaseous combustion products which is passed from said second regeneratorat less than 65:35 and greater than 45:55; and (2) (i) passing a firstamount of gaseous combustion products from the furnace into and througha cooled third regenerator to heat the third regenerator and cool saidfirst amount of gaseous combustion products, (ii) passing a secondamount of gaseous combustion products from the furnace into and througha cooled fourth regenerator to heat the fourth regenerator and cool saidsecond amount of gaseous combustion products, (iii) passing reformingfuel into a heated first regenerator to heat the reforming fuel and coolthe first regenerator, (iv) passing gaseous oxidant into and through aheated second regenerator to heat the gaseous oxidant and cool thesecond regenerator, and (v) passing said heated reforming fuel from saidfirst regenerator into said furnace, passing said heated gaseous oxidantfrom the second regenerator into the furnace, and combusting the heatedreforming fuel and said heated gaseous oxidant in the furnace; whilemaintaining the ratio of the molar flow rate of said first amount ofcooled gaseous combustion products which is passed from said firstregenerator to the molar flow rate of said cooled second amount ofgaseous combustion products which is passed from said second regeneratorat less than 65:35 and greater than 45:55.
 5. The method of claim 2wherein the molar ratio of cooled gaseous combustion products toreforming fuel in one or both of steps (B)(1)(iii) and (B)(2)(iii) isbetween 0.5 and 1.5 and said ratio of the molar flow rate of said cooledfirst amount of gaseous combustion products which is passed from saidfirst regenerator to the molar flow rate of said cooled second amount ofgaseous combustion products which is passed from said second regeneratoris from 55:45 to 65:35.
 6. The method of claim 2 wherein the molar ratioof cooled gaseous combustion products to reforming fuel in one or bothof steps (B)(1)(iii) and (B)(2)(iii) is up to 0.5 and said ratio of themolar flow rate of said cooled first amount of gaseous combustionproducts which is passed from said first regenerator to the molar flowrate of said cooled second amount of gaseous combustion products whichis passed from said second regenerator is from 50:50 to 60:40.
 7. Themethod of claim 1 wherein at the end of steps (B) (1)(iii) and (B)(1)(v)the flows of said reforming fuel to said third regenerator and of saidoxidant to said fourth regenerator are terminated and gaseous combustionproducts from the furnace are flowed through said third and fourthregenerators so that syngas in the third regenerator and oxidant in thefourth regenerator are expelled to the furnace and combusted tocompletion, and wherein at the end of steps (B) (2)(iii) and (B)(2)(v)the flows of said reforming fuel to said first regenerator and of saidoxidant to said second regenerator are terminated and gaseous combustionproducts from the furnace are flowed through said first and secondregenerators so that syngas in the first regenerator and oxidant in thesecond regenerator are expelled to the furnace and combusted tocompletion.
 8. The method of claim 2 wherein at the end of steps (B)(1)(iii) and (B)(1)(v) the flows of said reforming fuel to said thirdregenerator and of said oxidant to said fourth regenerator areterminated and gaseous combustion products from the furnace are flowedthrough said third and fourth regenerators so that syngas in the thirdregenerator and oxidant in the fourth regenerator are expelled to thefurnace and combusted to completion, and wherein at the end of steps (B)(2)(iii) and (B)(2)(v) the flows of said reforming fuel to said firstregenerator and of said oxidant to said second regenerator areterminated and gaseous combustion products from the furnace are flowedthrough said first and second regenerators so that syngas in the firstregenerator and oxidant in the second regenerator are expelled to thefurnace and combusted to completion.
 9. The method of claim 3 wherein atthe end of steps (B) (1)(iii) and (B)(1)(iv) the flows of said reformingfuel to said third regenerator and of said oxidant to said fourthregenerator are terminated and gaseous combustion products from thefurnace are flowed through said third and fourth regenerators so thatsyngas in the third regenerator and oxidant in the fourth regeneratorare expelled to the furnace and combusted to completion, and wherein atthe end of steps (B) (2)(iii) and (B)(2)(iv) the flows of said reformingfuel to said first regenerator and of said oxidant to said secondregenerator are terminated and gaseous combustion products from thefurnace are flowed through said first and second regenerators so thatsyngas in the first regenerator and oxidant in the second regeneratorare expelled to the furnace and combusted to completion.
 10. The methodof claim 4 wherein at the end of steps (B) (1)(iii) and (B)(1)(iv) theflows of said reforming fuel to said third regenerator and of saidoxidant to said fourth regenerator are terminated and gaseous combustionproducts from the furnace are flowed through said third and fourthregenerators so that syngas in the third regenerator and oxidant in thefourth regenerator are expelled to the furnace and combusted tocompletion, and wherein at the end of steps (B) (2)(iii) and (B)(2)(iv)the flows of said reforming fuel to said first regenerator and of saidoxidant to said second regenerator are terminated and gaseous combustionproducts from the furnace are flowed through said first and secondregenerators so that syngas in the first regenerator and oxidant in thesecond regenerator are expelled to the furnace and combusted tocompletion.
 11. The method of claim 1 wherein said difference intemperatures of the combustion products passing out of said first andsecond regenerators is maintained at 100 F or less and said differencein temperatures of the combustion products passing out of said third andfourth regenerators is maintained at 100 F or less.
 12. The method ofclaim 3 wherein said difference in temperatures of the combustionproducts passing out of said first and second regenerators is maintainedat 100 F or less and said difference in temperatures of the combustionproducts passing out of said third and fourth regenerators is maintainedat 100 F or less.
 13. The method of claim 3 wherein at the end of step(B) (1)(iii) the flow of said reforming fuel to said third regeneratoris terminated and gaseous combustion products from said furnace areflowed through said third regenerator into the furnace to reduce theamount of soot present in the third regenerator, and wherein at the endof step (B) (2)(iii) the flow of said reforming fuel to said firstregenerator is terminated and gaseous combustion products from saidfurnace are flowed through said first regenerator into the furnace toreduce the amount of soot present in the first regenerator.
 14. Themethod of claim 4 wherein at the end of step (B) (1)(iii) the flow ofsaid reforming fuel to said third regenerator is terminated and gaseouscombustion products from said furnace are flowed through said thirdregenerator into the furnace to reduce the amount of soot present in thethird regenerator, and wherein at the end of step (B) (2)(iii) the flowof said reforming fuel to said first regenerator is terminated andgaseous combustion products from said furnace are flowed through saidfirst regenerator into the furnace to reduce the amount of soot presentin the first regenerator.
 15. The method of claim 1 wherein at the endof step (B) (1)(iii) the flow of said reforming fuel to said thirdregenerator is terminated while letting the flow of gaseous combustionproducts continue to flow through the third regenerator to reduce theamount of soot present therein, and wherein at the end of step (B)(2)(iii) the flow of said reforming fuel to said first regenerator isterminated while letting the flow of gaseous combustion productscontinue through the first regenerator to reduce the amount of sootpresent therein.
 16. The method of claim 2 wherein at the end of step(B) (1)(iii) the flow of said reforming fuel to said third regeneratoris terminated while letting the flow of gaseous combustion productscontinue to flow through the third regenerator to reduce the amount ofsoot present therein, and wherein at the end of step (B) (2)(iii) theflow of said reforming fuel to said first regenerator is terminatedwhile letting the flow of gaseous combustion products continue throughthe first regenerator to reduce the amount of soot present therein. 17.The method of claim 1 wherein said reforming fuel is natural gas. 18.The method of claim 2 wherein said reforming fuel is natural gas. 19.The method of claim 3 wherein said reforming fuel is natural gas. 20.The method of claim 4 wherein said reforming fuel is natural gas. 21.The method of claim 1 wherein said gaseous oxidant contains 80 to 100vol. % O2.
 22. The method of claim 2 wherein said gaseous oxidantcontains 80 to 100 vol. % O2.
 23. The method of claim 3 wherein saidgaseous oxidant contains 80 to 100 vol. % O2.
 24. The method of claim 4wherein said gaseous oxidant contains 80 to 100 vol. % O2.